Method and apparatus for estimating direction of arrival using generation of virtual received signals

ABSTRACT

A received signal DOA estimation method using generation of virtual received signals includes: generating a preset number of virtual antennas at preset positions of a plurality of actual antennas; generating received signals received from the virtual antennas; and generating a DOA estimation value through a DOA estimation algorithm using the received signals received from the virtual antennas and the received signals received from the actual antennas.

CROSS-REFERENCES TO RELATED APPLICATIONS

The present application claims priority to Korean application number10-2018-0002532, filed on Jan. 8, 2018, which is incorporated byreference in its entirety.

BACKGROUND OF THE INVENTION

The present invention relates to a method and an apparatus forestimating a direction of arrival (DOA) using generation of virtualreceived signals, and more particularly, to a method and an apparatusfor estimating a DOA using generation of virtual received signals, whichare capable of estimating a DOA by generating a non-uniform linear array(NLA) using a virtual antenna based on a uniform linear array (ULA).

In a vehicle radar, when two vehicles in front are adjacent to eachother at the same distance from a radar sensor, the radar must be ableto recognize that there are two vehicles ahead, not one vehicle. It isimportant to accurately estimate a DOA of a received signal receivedfrom a target so as to separate multiple targets if the speeds andranges of the targets are similar. High resolution received signal DOAestimation algorithms, such as a multiple signal classification (MUSIC)algorithm and an estimation of signal parameters via rotationalinvariance technique (ESPRIT) algorithm, have been studied for decades.Recently, a Bartlett algorithm, which is less influenced by asignal-to-noise ratio (SNR) than a MUSIC algorithm, has received muchattention and is widely used.

When searching for a target using an ULA-type antenna, a narrow mainbeam width and a low side lobe are required to achieve preciseresolution and high accuracy. When the aperture of the antenna array iswide, the beam width of the main lobe is narrow. The narrow beam widthcan identify closely adjacent targets. However, side lobes and gratinglobes may occur and prevent positioning of the target. Further, the wideaperture of the antenna array occupies an excessively large space.

The background art of the present invention is disclosed in KoreanPatent Application Publication No. 10-2016-0134436 (Nov. 23, 2016)entitled “Direction-of-Angle Estimation Apparatus and Direction-of-AngleEstimation Method Using the Same”.

SUMMARY OF THE INVENTION

It is preferable to increase the number of antennas so as to increasethe resolution in measuring the DOA of the received signal of the radar.However, if the number of actual physical antennas is increased, thespace occupied by the antennas becomes wider. Therefore, instead ofincreasing the number of actual antennas, it is possible to obtain theeffect of increasing the total number of antennas by making a virtualantenna using the actual antennas, but this method has limitationsbecause the number of virtual antennas that can be increased isinfluenced by the number of actual antennas.

Embodiments of the present invention are directed to a method and anapparatus for estimating a DOA of a received signal using generation ofvirtual received signals, capable of increasing the number of virtualantennas that can be extended in a ULA antenna environment as comparedwith the related art, having a narrow beam width and a low side lobe ata limited antenna aperture size, generating no grating lobe, and furtherimproving a DOA resolution of a received signal.

In one embodiment, a received signal DOA estimation method usinggeneration of virtual received signals may include: generating a presetnumber of virtual antennas at preset positions of a plurality of actualantennas; generating received signals received from the virtualantennas; and generating a DOA estimation value through a DOA estimationalgorithm using the received signals received from the virtual antennasand the received signals received from the actual antennas.

The virtual antennas may be disposed between the actual antennas oroutside the actual antennas.

The virtual antennas may be disposed at unequal intervals, regardless ofthe positions of the actual antennas.

The set number may be set considering at least a signal-to-noise ratio(SNR) and the interval of the antennas.

The generating of the virtual antennas may include: setting a sectoraccording to a field of view (FOV) angle range, generating a transformmatrix through the set sector, and generating the received signalsreceived from the virtual antennas by using the generated transformmatrix; generating a correlation matrix by combining the receivedsignals received from the virtual antennas and the received signalsreceived from the actual antennas, generating an angle estimationspectrum by using the generated correlation matrix, and generating a DOAestimation value; and determining the set position by using a root meansquare error (RMSE) of the DOA estimation value.

The determining of the set position may include determining the setposition based on at least one of accuracy of the DOA estimation valueand an area of a side lobe and a grating lobe.

The transform matrix may be obtained by using a linear least square(LLS) method based on a relationship between the received signals.

The DOA estimation algorithm may be a Bartlett pseudo algorithm.

In another embodiment, a received signal DOA estimation apparatus usinggeneration of virtual received signals may include: a ULA receptionantenna including a plurality of actual antennas; a reception unitconfigured to extract a predetermined signal from received signalsreceived through the actual antennas of the ULA reception antenna andconvert the extracted signal into a digital signal; and a signalprocessing unit configured to receive the digital signal from thereception unit, generate received signals received from a preset numberof virtual antennas disposed at preset positions, and generate a DOAestimation value through a DOA estimation algorithm by using thereceived signals received from the actual antennas and the receivedsignals received from the virtual antennas.

The virtual antennas may be disposed between the actual antennas oroutside the actual antennas.

The virtual antennas may be disposed at unequal intervals, regardless ofthe positions of the actual antennas.

The set number may be set considering at least a signal-to-noise ratio(SNR) and the interval of the antennas.

The signal processing unit may be configured to set a sector accordingto a field of view (FOV) angle range, generate a transform matrixthrough the set sector, generate the received signals received from thevirtual antennas by using the generated transform matrix, generate acorrelation matrix by combining the received signals received from thevirtual antennas and the received signals received from the actualantennas, generate an angle estimation spectrum by using the generatedcorrelation matrix, generate a DOA estimation value; and determine theset position by using a root mean square error (RMSE) of the DOAestimation value.

The signal processing unit may be configured to determine the setposition based on at least one of accuracy of the DOA estimation valueand an area of a side lobe and a grating lobe.

The transform matrix may be obtained by using a linear least square(LLS) method based on a relationship between the received signals.

The DOA estimation algorithm may be a Bartlett pseudo algorithm.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a radio signal reception of a ULA antenna in which Nantennas are arranged in the form of a ULA.

FIG. 2 is a block diagram of a DOA estimation apparatus using generationof virtual received signals in accordance with an embodiment of thepresent invention.

FIG. 3 is a flowchart of a DOA estimation method using generation ofvirtual received signals in accordance with an embodiment of the presentinvention.

FIG. 4 is a diagram illustrating a specific execution procedure of stepS200 of the flowchart of FIG. 3.

FIG. 5 is a diagram illustrating a specific execution procedure of stepS400 of the flowchart of FIG. 3.

FIG. 6 is a diagram illustrating a specific execution procedure of stepS500 of the flowchart of FIG. 3.

FIG. 7 is a diagram illustrating a calculation process for a DOAestimation value.

FIG. 8 is a conceptual diagram illustrating a method of increasing avirtual antenna received signal using a virtual antenna in accordancewith an embodiment of the present invention.

FIG. 9 is a diagram illustrating a Bartlett pseudo spectrum when asector is set to [−15°, 15°] in accordance with an embodiment of thepresent invention.

FIG. 10 is a diagram illustrating a Bartlett pseudo spectrum when asector is set to [−5°, 5°] in accordance with an embodiment of thepresent invention.

FIG. 11 is a graph illustrating a change in a mean square root error inaccordance with an embodiment of the present invention.

DESCRIPTION OF SPECIFIC EMBODIMENTS

As is traditional in the corresponding field, some exemplary embodimentsmay be illustrated in the drawings in terms of functional blocks, units,and/or modules. Those of ordinary skill in the art will appreciate thatthese block, units, and/or modules are physically implemented byelectronic (or optical) circuits such as logic circuits, discretecomponents, processors, hard-wired circuits, memory elements, wiringconnections, and the like. When the blocks, units, and/or modules areimplemented by processors or similar hardware, they may be programmedand controlled using software (e.g., code) to perform various functionsdiscussed herein. Alternatively, each block, unit, and/or module may beimplemented by dedicated hardware or as a combination of dedicatedhardware to perform some functions and a processor (e.g., one or moreprogrammed processors and associated circuitry) to perform otherfunctions. Each block, unit, and/or module of some exemplary embodimentsmay be physically separated into two or more interacting and discreteblocks, units, and/or modules without departing from the scope of theinventive concept. Further, blocks, units, and/or module of someexemplary embodiments may be physically combined into more complexblocks, units, and/or modules without departing from the scope of theinventive concept.

Hereafter, a method and an apparatus for estimating a direction ofarrival (DOA) using generation of virtual received signals in accordancewith an embodiment of the present invention will be described in detailwith reference to the accompanying drawings. It should be noted that thedrawings are not to precise scale and may be exaggerated in thickness oflines or sizes of components for descriptive convenience and clarityonly. Furthermore, the terms as used herein are defined by takingfunctions of the invention into account and can be changed according tothe custom or intention of users or operators. Therefore, definition ofthe terms should be made according to the overall disclosures set forthherein.

FIG. 1 illustrates a radio signal reception of a ULA antenna in which Nantennas are arranged in the form of a ULA, FIG. 2 is a block diagram ofa DOA estimation apparatus using generation of virtual received signalsin accordance with an embodiment of the present invention, FIG. 3 is aflowchart of a DOA estimation method using generation of virtualreceived signals in accordance with an embodiment of the presentinvention, FIG. 4 is a diagram illustrating a specific executionprocedure of step S200 of the flowchart of FIG. 3, FIG. 5 is a diagramillustrating a specific execution procedure of step S400 of theflowchart of FIG. 3, FIG. 6 is a diagram illustrating a specificexecution procedure of step S500 of the flowchart of FIG. 3, FIG. 7 is adiagram illustrating a calculation process for a DOA estimation value,and FIG. 8 is a conceptual diagram illustrating a method of increasing avirtual antenna received signal using a virtual antenna in accordancewith an embodiment of the present invention.

FIG. 1 illustrates that N antennas receive radio signals reflected froma front target in ULA antennas spaced apart at an equal interval d in arow. In such ULA antennas, a received signal x(t) can be expressed asfollows:x(t)=As(t)+n(t)  (1)

x(t)=[x₁(t), x(₂(t), . . . x_(N)(t)]^(T), [.]^(T) is a transposeoperator, and N is the number of antennas. A=[a(θ₁), a(θ₂), . . .a(θ_(L))] is a steering matrix. The steering matrix is composed of asteering vector a(θ₁) as follows:

$\begin{matrix}{{a\left( \theta_{i} \right)} = \left\lbrack {e^{j\frac{2\;\pi}{\lambda}d_{1}{si}\; n\;\theta_{i}},e^{j\frac{2\;\pi}{\lambda}d_{2}{si}\; n\;\theta_{i}},\ldots\mspace{14mu},e^{j\frac{2\;\pi}{\lambda}d_{N}{si}\; n\;\theta_{i}}} \right\rbrack^{T}} & (2)\end{matrix}$

L is the number of targets, λ is a wavelength of a receives signal of anantenna, d_(i), is a distance to an i^(th) antenna, d₁=0, d₂=d, . . . ,d_(N)=(N−1)d since ULA is used in the embodiment of the presentinvention, and d is an antenna interval. s(t)=[s₁, s₂(t), . . . ,s_(L)(t)]^(T) represents a Lx1 incident signal vector at time t,n(t)=[n₁(t), n₂(t), . . . , n_(N)(t)]^(T) represents a zero mean whiteGaussian noise vector, and θ_(i) is an angle formed by a straight lineforming a right angle with an extension line of a ULA antennaarrangement and an incident signal vector received from each antenna.

An autocorrelation matrix of a received signal may be estimated asfollows:R _(xx=E[x() t)·x ^(H)(t)]  (3)

E[.]represents an expectation, R_(xx) represents a correlation matrix ofa receives signal x^((t)), and (.)^(H) represents a conjugate transposeoperation. If a signal is ergodic (after a significant time elapses, onesystem is in a condition that returns to a state almost similar to aninitial state), an ensemble average can be expressed as time average,and thus a self correlation matrix R_(xx) can be calculated using thetime average.

$\begin{matrix}{R_{xx} = {\frac{1}{K}{\sum{{x(t)} \cdot {x^{H}(t)}}}}} & (4)\end{matrix}$

K is the number of time samples.

The goal of the Bartlett algorithm is to determine a weighted vectorthat maximizes power of a received signal while constantly maintainingthe magnitude of noise. An array output can be expressed as a valueobtained by multiplying a weighted vector w by a received signal.y(t)=w ^(H) x(t)  (5)

w is an Nx1 weighted vector, and y(t) is a weighted output of a receivedsignal. If there is a signal incoming at an angle θ, an array output canbe expressed as follows:

$\begin{matrix}\begin{matrix}{{p(w)} = {{\max\limits_{w}{E\left\lbrack {{y(t)}}^{2} \right\rbrack}} = {\max\limits_{w}\left\lbrack {{w^{H}{x(t)}}}^{2} \right\rbrack}}} \\{= {\max\limits_{w}{w^{H}{E\left\lbrack {{{a(\theta)}{s(t)}{s^{H}(t)}{a^{H}(\theta)}} + {{n(t)}{n^{H}(t)}}} \right\rbrack}w}}} \\{= {\max\limits_{w}{\left\{ {{{E\left\lbrack {{s(t)}}^{2} \right\rbrack}{{w^{H}{a(\theta)}}}^{2}} + {\sigma_{n}^{2}{w}^{2}}} \right\}.}}}\end{matrix} & (6)\end{matrix}$

E[n(t)n^(H)(t)]=σ_(n) ²I, σ_(n) ² and represents a noise dispersion.|w|=1 so as to constantly maintain the magnitude of the noise component.Therefore, the solution of Equation (6) is as follows:

$\begin{matrix}{w = \frac{a(\theta)}{\sqrt{{a^{H}(\theta)}{a(\theta)}}}} & (7)\end{matrix}$

An output spectrum of a Bartlett algorithm can be expressed as follows:

$\begin{matrix}{{P(\theta)} = \frac{{a^{H}(\theta)}R_{xx}{a(\theta)}}{{a^{H}(\theta)}{a(\theta)}}} & (8)\end{matrix}$

FIG. 2 is a block diagram of a DOA estimation apparatus using generationof virtual received signals in accordance with an embodiment of thepresent invention.

The DOA estimation apparatus using generation of virtual receivedsignals in accordance with an embodiment of the present invention mayinclude a reception unit 40 connected to a ULA reception antenna 30, atransmission unit 20 connected to a ULA transmission antenna 10, and asignal processing unit 50 connected to the transmission unit 20 and thereception unit 40. The radar system 10 may further include a userinterface 30 connected to the signal processing unit 50.

Each of the ULA reception antenna 30 and the ULA transmission antenna 10may include a plurality of antennas. In particular, the ULA receptionantenna 30 may have a ULA antenna arrangement in which a plurality ofantennas are arranged at an equal interval in a row. A reflected signalreturned when a radio frequency signal transmitted through thetransmission antenna 10 is reflected from a front target may be receivedby the ULA reception antenna 30.

The transmission unit 20 wirelessly transmits a radar signal to thefront target through the transmission antenna 10. In one embodiment, thetransmission unit 20 may include a waveform generator 24, an oscillator26, and a power amplifier 28. The waveform generator 24 may generate asignal having an analog waveform having a desired period and shape,based on a digital transmission signal provided by the signal processingunit 50. For example, the signal generator 24 may provide a demodulatedsignal (triangular wave) having a triangular waveform to the oscillator26 as a transmission signal. The oscillator 26 may convert thetransmission signal generated by the waveform generator 24 into a radiofrequency (RF) signal having a high frequency in order for wirelesstransmission. For example, the oscillator 26 may perform frequencymodulation of the transmission signal provided by the waveform generator24. In addition, the oscillator 26 may provide the converted RF signalto a mixer 44 of the reception unit 40 as a reference signal. The poweramplifier 28 may amplify the RF signal output by the oscillator 26 intopower necessary for transmission and provide the amplified RF signal tothe transmission antenna 10. The oscillator 26 may be configured by, forexample, a voltage control oscillator (VCO).

The reception unit 40 receives the RF signal, which is reflected andreturned from the front target after transmitted from the transmissionantenna 10, through the reception antenna 30. The reception unit 40 maydown-convert the RF signal based on the reference signal provided fromthe oscillator 26 of the transmission unit 20, convert thedown-converted RF signal into a digital signal, and provide the digitalsignal to the signal processing unit 50. In one embodiment, thereception unit 40 may include a low-noise amplifier (LNA) 42, a mixer44, and an analog-to-digital converter (ADC) 48 for each antennaconstituting the reception antenna 30.

The low-noise amplifier 42 is connected to a corresponding antenna ofthe ULA reception antenna 30 and amplifies a slight reception signalreceived by the ULA reception antenna 30. The reception signal amplifiedby the low-noise amplifier 42 is provided to the mixer 44. The mixer 44may down-convert the reception signal based on a frequency differencebetween the amplified reception signal and the RF signal provided fromthe oscillator 26 of the transmission unit 20. That is, the mixer 44mixes the amplified reception signal and the RF signal provided from theoscillator 26 of the transmission unit 20, calculates a frequencydifference between the two signals, and obtains a beat signal having thecalculated difference frequency as a frequency. The beat signal obtainedby the mixer 44 is converted into a digital signal by the ADC 48. Theobtained digital reception signal is provided to the signal processingunit 50. The reception unit 40 may further include a low-pass filter(LPF) 46 for removing a low frequency component included in the beatsignal output from the mixer 44.

In one embodiment, the signal processing unit 50 may control the overalloperations of the transmission unit 20, the reception unit 40, and theuser interface 30. The signal processing unit 50 may receive, from thereception unit 40, digital information corresponding to the signalreflected from the front target, perform arithmetic processing accordingto a method described below, and estimates a DOA of the received signalreceived from the front target. In addition, the signal processing unit50 performs signal processing to generate information to be transmittedto the target through the transmission antenna 70, and provides theinformation to the transmission unit 20. The signal processing unit 50may be implemented by, for example, a digital signal processor (DSP), amicrocomputer, or the like.

The user interface (UI) 30 displays the processing result of the signalprocessing unit 50 or transmits a user instruction to the signalprocessing unit 50.

The configuration of the radar system 10 illustrated in FIG. 2 is merelyan example, and may have other configurations according to modulationand demodulation schemes of the radio signal, or the like. The radarsystem 10 may be used as a vehicle radar device installed in a vehicle.

The virtual antenna signal generation method in accordance with thepresent invention may be implemented by a program. The program may beembedded in the signal processing unit 50 and executed thereby.

FIG. 3 is a flowchart of a process of estimating a DOA of a receivedsignal based on a method in accordance with the present invention. FIG.7 is illustrates a calculation process of estimating a DOA of a receivedsignal based on a method in accordance with the present invention in thesignal processing unit 50 of the radar system 10 of FIG. 2.

A method for estimating a DOA of a received signal in accordance withthe present invention in the radar system 10 will be schematicallydescribed. In the radar system 10, the transmission unit 20 generates anRF signal and transmits the RF signal through the transmission antenna10 based on a digital transmission signal provided by the signalprocessing unit 50. The RF signal transmitted to the target bytransmission antenna 10 is collided and reflected from the front target.Each antenna of the ULA reception antenna 30 may receive the RF signalreflected and returned from the target, and transmit the RF signal tothe reception unit 40. As described above, the reception unit 40generates a beat signal based on a frequency difference between the RFsignal received by each antenna 30 and the RF signal provided from theoscillator 26, convert the beat signal into a digital signal, andprovides the digital signal to the signal processing unit 50 (stepS100).

The reception signal provided to the signal processing unit 50 by thereception unit 40 is a time-domain signal. The time-domain signal isconverted into a frequency-domain signal (step S200). The flowchartillustrated in FIG. 4 shows a detailed execution procedure of step S200of the flowchart illustrated in FIG. 3. Referring to FIG. 4, thetime-domain signal provided by the reception unit 40 may be convertedinto a complex signal using a Hilbert transform algorithm by the signalprocessing unit 50 (step S210). Then, the converted complex signal maybe converted into a frequency-domain signal using a fast Fouriertransform (FFT) algorithm (step S220). Calibration processing may beperformed on the converted frequency-domain signal (step S230).

The signal corresponding to the beat frequency among the signalsconverted into the frequency domain may be converted again into thetime-domain signal (step S400). The flowchart of FIG. 5 shows a detailedexecution procedure of step S400. Referring to FIG. 5, the beatfrequency signal is extracted from the frequency-domain signal obtainedthrough the Fourier transform (step S310). Inverse fast Fouriertransform (IFFT) is performed on the extracted beat frequency signal andthe beat frequency signal is converted into the time-domain signal (stepS420).

When the time-domain signal is obtained in this manner, a virtualreceived signal received through a virtual antenna is generated by usingthe converted time-domain signal (step S500).

When the virtual received signals of the desired number of virtualantennas are obtained, an algorithm for received signal DOA estimationis performed by using the virtual received signals and the receivedsignal received through the actual physical antenna together (stepS300).

In the embodiment of the present invention, the improved received signalDOA estimation algorithm is proposed which increases the resolution ofthe Bartlett algorithm by using the DOA estimation value by performingthe DOA estimation algorithm, and reduces the level of the grating lobeand the side lobe. The conventional arrangement interpolation algorithmmust sect a sector indicating a viewing range. When a target existsoutside the sector, the conventional interpolation algorithm cannotaccurately estimate the position of the target. In addition, anadditional step must be performed so as to set the initial sector.

FIG. 6 is a diagram illustrating a specific execution procedure of stepS500 of the flowchart of FIG. 3.

Referring to FIGS. 6 and 8, the execution procedure of step S500 ofgenerating the virtual received signal will be described in more detail.FIG. 8 conceptually illustrates the method of the present inventionwhich, when the ULA reception antenna 30 is implemented by four actualantennas arranged in a ULA form, generates the reception signals of thevirtual antennas while the virtual antenna increases using the receptionsignals of the four actual antenna, and determines the optimum virtualantenna position, that is, the set position, based on them. The process(step S500) of generating the virtual reception signal will be describedin more detail with reference to FIGS. 6 and 8.

First, as illustrated in FIG. 8A, when M actual antennas exist, a setnumber of virtual antennas are generated (S410).

The set number is the number of virtual antennas whose angularresolution has the maximum performance. In the present embodiment, fourvirtual antennas are employed.

The virtual antennas may be previously generated at various positions.For example, the virtual antennas may be arranged between actualantennas or outside the actual antennas by applying interpolation orextrapolation.

In addition, the virtual antennas may be arranged in unequal intervals,regardless of the position of the actual antenna.

A sector for using interpolation according to a field of view (FOV) of aradar is designated, and a transform matrix T is generated according toa schematic target angle primarily obtained with the set number ofvirtual antennas (S420). That is, the sector is primarily defined, and asecondary angel is readjusted with respect to the first estimated angle.As the sector is defined closely to the position of the actual target,the angle estimatio performance may be improved. In this case, the angleof the target may be estimated through a beamforming method.

As the sector is designated as described above, the reception signalreceived by the virtual antenna is generated by using the transformmatrix T obtained through the sector.

In FIG. 8B, one of the set number of virtual antennas, that is, fourvirtual antennas, is disposed on the right side of the leftmost actualantenna by interpolation, and the remaining three antennas are disposedoutside the actual antenna by extrapolation.

Meanwhile, as the signal received by the virtual antenna is generated,the signal received by the virtual antenna is mixed with the signalreceived by the actual antenna to generate a new correlation matrix, theangle estimation spectrum is generated by using the correlation matrix,and the angle is estimated through the angle estimation spectrum. In thepresent embodiment, the Bartlett pseudo spectrum may be employed as theDOA estimation algorithm.

Then, as illustrated in FIG. 7, a DOA estimation algorithm for receivedsignal DOA estimation is performed by using the virtual received signalsand the received signal received through the actual physical antennatogether. The Bartlett pseudo spectrum may be employed as the DOAestimation algorithm.

As such, if the DOA estimation value is generated through the DOAestimation algorithm, the optimal combination, that is, the position ofthe virtual antenna, is set by using the root mean square error (RMSE)of the angle.

That is, as the condition for setting the position of the virtualantenna, the position having the best performance may be set as the setposition as illustrated in FIG. 8C, based on the accuracy of the DOAestimation value and the area of the side lobe and the grating lobe.

For example, in a case in which the interval of the actual antennas is1.8λ, if four virtual antennas are arranged at an interval of 0.1λ, atotal of 8,214,570 combinations may be generated.

When the processes illustrated in FIG. 6 are performed on the generatedcombinations, the optimal combination may be determined based on theaccuracy of the DOA estimation value and the area of the side lobe andthe grating lobe.

TABLE 1 Area of grating lobe and side lobe with respect to eachcombination, and maximum angular resolution GL/SL Maximum angular d′₁d′₂ d′₃ d′₄ area resolution 1 1.0λ 6.2λ 7.0λ 8.7λ 77.01 6° 2 2.5λ 6.2λ7.0λ 8.7λ 81.41 6° 3 4.4λ 6.1λ 8.6λ 8.6λ 81.46 6° 4 1.0λ 6.2λ 8.9λ 8.9λ96.99 6° 5 1.0λ 6.2λ 9.0λ 9.0λ 98.01 6°

In Table 1, d′₁ to d′₄ are positions of virtual antennas and correspondto the distance from the actual antenna disposed at the outermost amongactual antennas. The GL/SL area is an area of grating lobe and sidelobe.

Table 1 shows five combinations having the best performance among the8,214,570 combinations.

In the above-described embodiment, since the interval of the actualantennas is 1.8λ, the total interval between four actual antennas is5.4λ.

Therefore, in the case of the first, fourth, and fifth combinations, d′₁is disposed between the first actual antenna and the second actualantenna (interpolation), and d′₂ to d′₄ are disposed outside the actualantenna (extrapolation).

In the second combination, d′₁ is disposed between the second actualantenna and the third actual antenna, and d′₂ to d′₄ are disposedoutside the actual antenna.

In the third combination, d′₁ is disposed between the third actualantenna and the fourth actual antenna, and d′₂ to d′₄ are disposedoutside the actual antenna.

Compared with the first combination to the fifth combination, themaximum angular resolutions of the first combination to the fifthcombination are the same, but the first combination has the bestperformance since the first combination has the smallest area of thegrating lobe and the side lobe.

Therefore, the positions of the four virtual antennas may be 1.0λ, 6.2λ,7.0λ, and 8.7λ.

In accordance with embodiments of the present invention, the method forgenerating the virtual received signal using generation of virtualreceived signals can estimate DOA of the received signal at highresolution by applying the target detection radar device.

FIG. 9 is a diagram illustrating a Bartlett pseudo spectrum when asector is set to [−15°, 15°] in accordance with an embodiment of thepresent invention, FIG. 10 is a diagram illustrating a Bartlett pseudospectrum when a sector is set to [−5°, 5°] in accordance with anembodiment of the present invention, and FIG. 11 is a graph illustratinga change in a mean square root error in accordance with an embodiment ofthe present invention.

FIG. 9 is a Bartlett pseudo spectrum when the sector is set to [−15°,15°], and FIG. 10 is a Bartlett pseudo spectrum when the sector is setto [−5°, 5°]. As the sector is closer to the section in which the actualtarget exists, better performance is exhibited.

In addition, referring to FIG. 11, compared with the performances ofthree arrays (12ULA, 4ULA, virtually expended array) having similararray aperture sizes, the performance of the proposed array isrelatively excellent. That is, as compared with the antennas to whichthe virtual antennas are not applied, the virtual antennas in accordancewith the embodiment of the present invention has relatively excellentRMSE performance. That is, when SNR is 10 dB, RMSE of the virtualantenna is 0.7°, RMSE of the actual antenna is 2.4°, and the accuracy ofthe DOA estimation value is increased by about 1.4° as compared with theactual antenna.

In accordance with embodiments of the present invention, the method andthe apparatus for estimating the DOA using generation of virtualreceived signals can generate a virtual antenna by using bothinterpolation and extrapolation so that the resolution can be ensuredeven when the antenna aperture size is small.

In addition, in accordance with embodiments of the present invention,the method and the apparatus for estimating the DOA using generation ofvirtual received signals can suppress the grating lobe while maintaininga high resolution.

Furthermore, in accordance with embodiments of the present invention,the method and the apparatus for estimating the DOA using generation ofvirtual received signals can be applied to the radar for the autonomousvehicle, can accurately recognize the number of actual vehicles throughthe improved resolution, without mistaking a plurality of vehicles nearthe front as one vehicle, can precisely monitor accurate forwardsurveillance, and can effectively prevent a vehicle collision accident.

Although preferred embodiments of the invention have been disclosed forillustrative purposes, those skilled in the art will appreciate thatvarious modifications, additions and substitutions are possible, withoutdeparting from the scope and spirit of the invention as defined in theaccompanying claims.

What is claimed is:
 1. A method for estimating a direction of arrival(DOA) of a received signal by generating a plurality of virtual receivedsignals, the method comprising: generating a preset number of virtualantennas at preset positions from a plurality of actual antennas;generating a plurality of virtual received signals received from thevirtual antennas; and generating a DOA estimation value through a DOAestimation algorithm using the virtual received signals received fromthe virtual antennas and received signals received from the actualantennas; wherein generating the virtual antennas comprises: setting asector according to a field of view (FOV) angle range, generating atransform matrix through the set sector, and generating the virtualreceived signals received from the virtual antennas by using thegenerated transform matrix; and generating a correlation matrix bycombining the received signals received from the virtual antennas andthe received signals received from the actual antennas, generating anangle estimation spectrum by using the generated correlation matrix, andgenerating the DOA estimation value.
 2. The method of claim 1, whereinthe virtual antennas are disposed between the actual antennas or outsidethe actual antennas.
 3. The method of claim 1, wherein the virtualantennas are disposed at unequal intervals, regardless of the positionsof the actual antennas.
 4. The method of claim 1, wherein the presetnumbers are set considering at least a signal-to-noise ratio (SNR) andintervals of the actual antennas.
 5. The method of claim 1, wherein thegenerating of the virtual antennas further comprises: determining thepreset positions by using a root mean square error (RMSE) of the DOAestimation value.
 6. The method of claim 1, further comprisingdetermining the preset positions based on at least one of accuracy ofthe DOA estimation value or an area of a side lobe and a grating lobe.7. The method of claim 1, wherein the transform matrix is obtained byusing a linear least square (LLS) method based on a relationship betweenthe received signals.
 8. The method of claim 1, wherein the DOAestimation algorithm is a Bartlett pseudo algorithm.
 9. An apparatusconfigured for estimation of a direction of arrival (DOA) of a receivedsignal by generation of virtual received signals, the apparatuscomprising: a uniform linear array (ULA) reception antenna comprising aplurality of actual antennas; a reception unit configured to extract apredetermined signal from received signals received through the actualantennas of the ULA reception antenna and convert the extracted signalinto a digital signal; and a signal processing unit configured toreceive the digital signal from the reception unit, generate virtualreceived signals received from a preset number of virtual antennasdisposed at preset positions, and generate a DOA estimation valuethrough a DOA estimation algorithm by using the received signalsreceived from the actual antennas and the virtual received signalsreceived from the virtual antennas; wherein the signal processing unitis configured to set a sector according to a field of view (FOV) anglerange, generate a transform matrix through the set sector, generate thevirtual received signals received from the virtual antennas by using thegenerated transform matrix, generate a correlation matrix by combiningthe virtual received signals received from the virtual antennas and thereceived signals received from the actual antennas, generate an angleestimation spectrum by using the generated correlation matrix, andgenerate the DOA estimation value.
 10. The apparatus of claim 9, whereinthe virtual antennas are disposed between the actual antennas or outsidethe actual antennas.
 11. The apparatus of claim 9, wherein the virtualantennas are disposed at unequal intervals, regardless of positions ofthe actual antennas.
 12. The apparatus of claim 9, wherein the presetnumbers are set considering at least a signal-to-noise ratio (SNR) andintervals of the actual antennas.
 13. The apparatus of claim 9, whereinthe signal processing unit is further configured to determine the presetpositions by using a root mean square error (RMSE) of the DOA estimationvalue.
 14. The apparatus of claim 9, wherein the signal processing unitis configured to determine the preset positions based on at least one ofaccuracy of the DOA estimation value or an area of a side lobe and agrating lobe.
 15. The apparatus of claim 9, wherein the transform matrixis obtained by using a linear least square (LLS) method based on arelationship between the received signals.
 16. The apparatus of claim 9,wherein the DOA estimation algorithm is a Bartlett pseudo algorithm.